Assigning a socket in timewait state to skb->sk can trigger
kernel oops, e.g. in nfnetlink_log, which does:

if (skb->sk) {
        read_lock_bh(&skb->sk->sk_callback_lock);
        if (skb->sk->sk_socket && skb->sk->sk_socket->file) ...

in the timewait case, accessing sk->sk_callback_lock and sk->sk_socket
is invalid.

Either all of these spots will need to add a test for sk->sk_state != TCP_TIME_WAIT,
or xt_TPROXY must not assign a timewait socket to skb->sk.

This does the latter.

If a TW socket is found, assign the tproxy nfmark, but skip the skb->sk assignment,
thus mimicking behaviour of a '-m socket .. -j MARK/ACCEPT' re-routing rule.

The 'SYN to TW socket' case is left unchanged -- we try to redirect to the
listener socket.

Cc: Balazs Scheidler <bazsi@balabit.hu>
Cc: KOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: NFlorian Westphal <fwestphal@astaro.com>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

Signed-off-by: NBalazs Scheidler <bazsi@balabit.hu>
Signed-off-by: NKOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

Also, inline this function as the lookup_type is always a literal
and inlining removes branches performed at runtime.
Signed-off-by: NBalazs Scheidler <bazsi@balabit.hu>
Signed-off-by: NKOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

Without tproxy redirections an incoming SYN kicks out conflicting
TIME_WAIT sockets, in order to handle clients that reuse ports
within the TIME_WAIT period.

The same mechanism didn't work in case TProxy is involved in finding
the proper socket, as the time_wait processing code looked up the
listening socket assuming that the listener addr/port matches those
of the established connection.

This is not the case with TProxy as the listener addr/port is possibly
changed with the tproxy rule.
Signed-off-by: NBalazs Scheidler <bazsi@balabit.hu>
Signed-off-by: NKOVACS Krisztian <hidden@balabit.hu>
Signed-off-by: NPatrick McHardy <kaber@trash.net>

The iptables tproxy core is a module that contains the common routines used by
various tproxy related modules (TPROXY target and socket match)
Signed-off-by: NKOVACS Krisztian <hidden@sch.bme.hu>
Signed-off-by: NPatrick McHardy <kaber@trash.net>